Manufacture of semiconductor integrated circuits and other micro-scale devices typically requires formation of multiple metal layers on a wafer or other substrate. By electroplating metals layers in combination with other steps, such as planarizing, etching and photolithography, patterned metal layers forming the micro-scale devices are created.
Electroplating is performed with the substrate, or one side of the substrate, in a bath of liquid electrolyte, and with electrical contacts touching a conductive layer on the substrate surface. Electrical current is passed through the electrolyte and the conductive layer. Metal ions in the electrolyte deposit or plate out onto the substrate, creating a metal film on the substrate. The metal ions also tend to plate out onto the electrical contacts as well. This affect, referred to as “plate-up”, changes the electric field around the contacts, causing non-uniform plating. The metal plated onto the electrical contacts consequently must be removed, adding to the time requirements and complexity of the manufacturing process.
So called dry or closed contact rings have been developed to avoid plate-up of the contacts. In these designs, a seal seals the electrolyte away from the electrical contacts. The seal contacts the substrate surface radially inwardly of the electrical contacts, so that the contacts remain isolated from the electrolyte. Industry specifications for plating with a sealed contact ring increasingly require that the annular band at the edge of the wafer covered by the seal must be as small as possible, currently towards about 1 mm. To plate wafers having a notch in the edge of the wafer (to indicate a specific crystal orientation of the wafer material), the seal correspondingly must have an inward protrusion at the notch to maintain a continuous seal against the wafer. During electroplating, electric current is crowded at the notch due to the irregular geometry. This causes the plated film to be thicker around the notch than at the rest of the wafer. The yield of the wafer may therefore be reduced since the thicker plated film around the notch may negatively affect subsequent processing steps.
Accordingly, engineering challenges remain in electroplating wafers and similar work pieces having edge irregularities, such as a notch.